Zoom lens system

Abstract

A zoom lens system which includes a positive first lens group and a negative second lens group, in this order from the object side; wherein zooming is performed by moving the first lens group and the second lens group, and by varying the distance between the first lens group and the second lens group; wherein the zoom lens system satisfies the following condition:wherein:fT designates the focal length of the entire lens system at the long focal-length extremity andf2G designates the focal length of the second lens group.

What is claimed is:  
     
       1. A zoom lens system consisting of a positive first lens group and a negative second lens group, in this order from the object side, wherein zooming is performed by moving said first lens group and said second lens group, and by varying the distance between said first lens group and said second lens group; 
       wherein said zoom lens system satisfies the following condition:  
       
         
           −7.0<f T /f 2G ≦−5.28  
         
       
       wherein:  
       f T  designates the focal length of the entire lens system at the long focal-length extremity; and  
       f 2G  designates the focal length of said second lens group.  
     
     
       2. The zoom lens system according to claim  1 , wherein said zoom lens system further satisfies the following condition: 
       
         
           4.2<f T /f 1G <6.0  
         
       
       wherein  
       f 1G  designates the focal length of said first lens group.  
     
     
       3. The zoom lens system according to claim  1 , wherein at least one lens element in said negative second lens group has an aspherical surface that satisfies the following condition: 
        0<ΔI ASP <3 
       wherein:  
       ΔI ASP  designates the variation of the spherical aberration coefficients of said aspherical surface when the focal length at the short focal-length extremity is assumed to be 1.0.  
     
     
       4. The zoom lens system according to claim  2 , wherein at least one lens element in said negative second lens group has an aspherical surface that satisfies the following condition: 
       
         
           0<ΔI ASP <3  
         
       
       wherein:  
       ΔI ASP  designates the variation of the spherical aberration coefficients of said aspherical surface when the focal length at the short focal-length extremity is assumed to be 1.0.  
     
     
       5. A zoom lens system comprising a positive first lens group and a negative second lens group, in this order from the object side, wherein zooming is performed by moving said first lens group and said second lens group, and by varying a distance between said first lens group and said second lens group; 
       wherein said zoom lens system satisfies the following relationships:  
       
         
           −7.0<f T /f 2G <5.1  
         
       
       
         
           4.2<f T /f 1G <6.0  
         
       
       wherein:  
       f T  designates a focal length of the entire zoom lens system at a long focal-length extremity;  
       f 2G  designates the focal length of said second lens group; and  
       f 1G  designates the focal length of said first lens group.  
     
     
       6. The zoom lens system according to claim  5 , wherein at least one lens element in said negative second lens group has an aspherical surface that satisfies the following relationship: 
       
         
           0<ΔI ASP <3  
         
       
       wherein:  
       ΔI ASP  designates the variation of the spherical aberration coefficients of said spherical surface when the focal length at the short focal-length extremity is assumed to be 1.0.